Ink jet printing is a conventional technique by which printing is accomplished without requiring contact between the printing apparatus (e.g., a printer, copier or multi-function apparatus) and the substrate, or medium, on which the desired print characters/marks are deposited. For example, a heater on an heater chip associated with a printhead installed in the printing apparatus can be selectively energized for vapor phase droplet formation in ink in an associated ink well. Such vapor phase droplet formation forms a bubble in the ink which causes a drop(s) of the ink to be ejected from a nozzle(s) associated therewith.
Printing a character or mark can be accomplished by energizing the heater (each time a drop is required at a position on the substrate/medium) for a sufficient period of time to generate such a bubble, cause the bubble's growth and cause an ink drop to be ejected from the nozzle(s) by the action of the bubble. One particular configuration of such a heater includes a resistive heating element applied to a substrate of a heater chip.
If a heater fails to heat the ink as desired, a corresponding nozzle(s) is often considered to have failed and/or be “missing.” While there are several causes of the failure of a heater to heat ink as desired, one particular cause is the heater element either breaks or fractures and goes to essentially an infinite resistance, thereby preventing the necessary flow of current. In the relevant art, a heater suffering from this type of failure is often generically and interchangeably referred to as either a “blown” heater or an “open” heater (both terms being interchangeably used hereinafter). As can be understood by one of ordinary skill in the art, a blown or open heater can also be used to describe a heater that is experiencing similar non-desired jetting characteristics, such as when the heater has an undesirably high resistance for any number of reasons.
It is desirable to be able to detect heaters that are not properly functioning on a heater chip. This information can be utilized by the printhead and/or printing apparatus/driver to, for example, minimize printing artifacts due to such malfunctioning/non-functioning heaters and/or alert the user of the need to replace the printhead/heater chip. As such, there is a need, for example, for a test circuit adapted to detect an open heater (or an otherwise open circuit containing the heater) on a heater chip. Accordingly, such test circuits on a heater chip and methods for using the same are desired.